Сумма квадрата косинуса и квадрата синуса равна 1, следовательно
cosA = √1-(1/4)^2 = √1-1/16 = √15/16
2) <span>-2 3/4 +(+ 6,8) + (- 1,25) + (+ 3 1/5) = -2 3/4 + 6,8 - 1,25 + 3 1/5 = -2 3/4 + 6 8/10 - 1 1/4 + 3 1/5 = -11/4 + 68/10 - 5/4 + 16/5 = -55/20 + 136/20 - 25/20 + 64/20 = 120/20 = 6
3) </span><span>- 5 1/6 + (+ 7 1/9) + (-4 1/3) + (-7 1/9) = -5 1/6 + 7 1/9 - 4 1/3 - 7 1/9 = -31/6 + 64/9 - 13/3 - 64/9 = -31/6 - 13/3 = -31/6 - 26/6 = -57/6 = -9 3/6 = -9 1/2
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AC(0-0;2-4;5+1)=(0;-2;6)
CB(1-0;3-2;0-5)=(1;1;-5)
AC-CB=(0-1;-2-1;6+5)=(-1;-3;11)
|AC-CB|=
=√1+9+121=√131
AB(-3-1;-1+1;2-0)=(-4;0;2)
CB(-3+1;-1-2;2-1)=(-2;-3;1)
AB-CB=(-4+2;0+3;2-1)=(-2;3;1)
|AB-CB|=
=√4+9+1=√14
= (1/4 * 7/10) * (216 * 1/216) = 7/40 * 1 = 7/40 = 0,175
= (4 1/3 * 3/13) * 6 1/5 = (13/3 * 3/13) * 6 1/5 = 1 * 6 1/5 = 6 1/5 = 6,2